In recent years, a micro-scale analysis channel or the like is formed on a small base plate (substrate), which is made from, for example, a silicon, silicone, glass or other materials, by a semiconductor microfabrication (fine processing) technology to provide a microchip. Such microchip is used as a microreactor to, for example, separate (isolate), synthesize (compose), extract (sample), and/or analyze a trace amount of reagent. Examples of microchip and methods of fabricating the microchip are disclosed in, for example, Patent Literature 1 (Japanese Patent Application Laid-Open Publication No. 2006-187730) and Patent Literature 2 (Japanese Patent No. 3714338).
The microchip has a channel or flow channel, which is often referred to as a microchannel. This channel includes a plurality of areas having prescribed functions respectively, such as a reaction area in which a reagent is placed. Accordingly, the microchips can be configured to suit for various applications. Typical applications of the microchip include analyses in the fields of chemistry, biology, pharmacy, medical science, and veterinary medicine (e.g., genetic analysis, clinical diagnosis, and drug screening), and also include composition synthesis as well as environmental measurement (monitoring).
Typically, the microchip has a pair of base plates that face each other and are bonded to each other, and also has a fine channel formed in the surface of at least one of the base plates. For example, the fine channel is 10 to several hundred μm in width and 10 to several hundred μm in depth. Conventional microchips generally use glass base plates because the glass base plates are easy to fabricate and are optically detectable. Recently developed microchips use resin base plates because the resin base plates are light in weight, difficult to break (as compared with the glass base plates), and inexpensive.
In the field of medical science, the microchip is used for measurements in the clinical (laboratory) test or the like when the measurements take advantage of intermolecular interaction such as immune reaction. Such measurements include, for example, the surface plasmon resonance (SPR) measurement, the quartz crystal microbalance (QCM) measurement, and the functional (functionalized) surface-based measurement. The functional surface is made from a material (e.g., from colloidal gold particle to ultrafine particle). Such microchip has an antibody that is fixed in, for example, the channel in advance. A reagent, which contains an antigen, is caused to flow in the channel such that an antibody-antigen reaction takes place. Measurements about the antibody-antigen reaction are carried out with the microchip.
FIG. 9(a) of the accompanying drawings schematically illustrates a microchip 10. FIG. 9(b) illustrates a cross-sectional view taken along the A-A line in FIG. 9(a). As shown in FIG. 9(a), the microchip 10 includes a pair of base plates (first microchip base plate 11 and a second microchip base plate 12) which face each other and are bonded to each other. The microchip 10 also includes a fine channel 14 that has an inlet 13a and an outlet 13b. The channel 14 is, for example, 10 to several hundred μm in width and 10 to several hundred μm in depth. Specifically, as shown in FIG. 9(b), the channel 14 is defined by a fine groove formed in the first microchip base plate 11, and the upper surface of the second microchip base plate 12. A metallic thin film 15 is disposed in the channel 14. The metallic thin film 15 is located on the upper surface of the second microchip base plate 12 in the channel (i.e., the bonding surface between the first and second base plates 11 and 12). The metallic thin film 15 includes a chrome (Cr) thin film and a gold (Au) thin film laminated on the chrome thin film.
Fixing the antibody in the channel 14 of the microchip is carried out by, for example, the following manner.
As shown in FIG. 10(a) of the accompanying drawings, a reagent solution feeding tube (filling pipe) 101 is fitted in the inlet 13a of the microchip 10. Likewise, a reagent solution discharge tube 102 is fitted in the outlet 13b of the microchip 10. A joint element 103 is attached to a free end of the reagent solution feeding tube 101, and another joint element 103 is attached to a free end of the reagent solution discharge tube 102. These joint elements 103 are connected to the inlet 13a and the outlet 13b, respectively.
Phosphate buffered saline (referred to as “PBS” hereinafter) is fed to the channel 14 of the microchip 10 from the reagent solution feeding tube 101 to clean the channel 14. The PBS that flows through the channel 14 is discharged to the outside from the reagent solution discharge tube 102, which is connected to the outlet 13b of the channel 14.
Referring next to FIG. 10(b), a solution to make an ASM (e.g., alkanthiol-containing solution) is fed to the channel 14 of the microchip 10 from the reagent solution feeding tube 101. Alkanthiol contained in the alkanthiol-containing solution reacts with the Au thin film, and an SAM film (Self-Assembled Monolayer film) 16 is formed on the Au thin film. The alkanthiol-containing solution that does not contribute to the formation of the SAM film is discharged to the outside through the reagent solution discharge tube 102.
Subsequently, as shown in FIG. 10(c), the PBS is fed to the channel 14 of the microchip 10 from the reagent solution feeding tube 101 to remove the remaining alkanthiol-containing solution from the channel 14. The PBS that flows through the channel 14 is discharged to the outside from the reagent solution discharge tube 102.
Then, as shown in FIG. 11(d) of the accompanying drawings, an antibody-containing solution is fed to the channel 14 of the microchip 10 from the reagent solution feeding tube 101. The antibody contained in the antibody-containing solution reacts with the alkanthiol SAM film 16 and chemically bonds to the alkanthiol SAM film 16 such that the antibody is fixed (secured) on the SAM film 16. Thus, the antibody Ig is fixed on the metallic thin film 15.
Because the floating antibody may remain on the surface of the antibody Ig fixed on the SAM film 16 and/or the antibody may stay in an area other than the SAM film 16 in the channel 14, the PBS is fed to the channel 14 of the microchip 10 from the reagent solution feeding tube 101, as shown in FIG. 11(e), to purge the remaining antibody with the PBS. The PBS that contains the residual antibody is discharged to the outside from the reagent solution discharge tube 102 that is connected to the outlet 13b of the channel 14.
In general, the antibody becomes inactive (deactivated) when the antibody contacts the air. Thus, after the residual antibody is purged with the PBS, the interior of the channel 14 is filled with the PBS, as shown in FIG. 11(f), to avoid the contact with the air. The inlet 13a and the outlet 13b of the microchip 10 are sealed by sealing members 104 (e.g., paraffin film or the like), respectively.